JPH08208232A - Sol-gel method synthesis of manganese oxide substance with octahedron structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermically stable manganese oxide material having an octahedral structure and a tunnel structure.

SOLUTION: A manganese oxide having an octahedral molecular structure is produced by the method which comprises; forming a solution containing permanganate anion; adding an organic reducing agent to the solution to form a gel; recovering gel without containing substantially an unreacted reducing agent and heating the gel at a temperature which is effective to produce the manganese oxide material.

COPYRIGHT: (C)1996,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a manganese oxide material having an octahedral structure. More specifically, the invention relates to the sol-gel synthesis of such manganese oxide materials with high thermal stability.

[0002]

2. Description of the Related Art Manganese oxide octahedral molecular sieves having a unidirectional tunnel structure constitute a group of molecular sieves in which chains of MnO ₆ octahedra share edges to form tunnel structures of different sizes. To do. Such substances have been detected in samples of land origin and have also been found in manganese nodules recovered from the ocean floor. Manganese nodules are used to oxidize carbon monoxide, methane and butane (US Pat. No. 3,214,236) and reduce nitric oxide with ammonia (Atmospheric Environment, V
ol. 6, p. 309 (1972)) and demetalization of atmospheric distillation bottoms in the presence of hydrogen (Ind. Eng. Chem. Proc. Dev.,
Vol. 13, p. 315 (1974)) is described as a useful catalyst.

Hollandite is a naturally occurring hydrous manganese oxide (also referred to as "framework hydrate") with a tunnel structure in which Mn can exist as Mn ⁴⁺ and other oxidation states. , The tunnels can differ in size and shape, and various monovalent or divalent cations can be present in the tunnel. The hollandite structure consists of double chains of MnO ₆ octahedra that share edges and form a (2 × 2) tunnel structure.
The average size of these tunnels is about 4.6 Å square. Ba, K, Na and Pb ions are present in the tunnel and are coordinated to the double chain oxygen. The type of tunnel cation determines the mineral species. Specific hollandite seeds include hollandite (BaMn ₈ O ₁₆ ), cryptomelane (KMn ₈ O ₁₆ ), and manjiroite (NaMn ₈
O ₁₆ ) and coronado (PbMn ₈ O ₁₆ ).

A hydrothermal method for synthesizing manganese oxide octahedral molecular sieves having a (2 × 2) tunnel structure like that of naturally occurring hollandite is Synthesis of M
icroporous Materials, Vol. II, 333, ML Occelli,
HE Robson, van Nostrand Reinhold, NY, 1992
"Hydrothermal Synthesis of Manganese Oxid
e with Tunnel Structures ”. Such a synthetic octahedral molecular sieve having a (2 × 2) tunnel structure is referred to in the art by the name OMS-2. The (2 × 2) tunnel structure of OMS-2 is shown in FIG.
Is schematically shown.

A hydrothermal method for producing OMS-2 is an aqueous solution of a manganese cation and a permanganate oxide anion,
80-1 in the presence of counter cations having an ionic diameter of 2.3-4.6Å under acidic conditions, ie pH <3
Pressurizing at a temperature in the range of 40 ° C. This counter cation can serve as a template material for the formation of the OMS-2 product and can be retained in its tunnel structure. According to analytical tests, OMS-2 produced by this method is thermally stable up to 600 ° C.

Alternatively, OMS-2 is R. Giovani
li and B. Balmer, Chimia, 35 (1981) 53. Therefore,
Reacting the manganese cation with the permanganate cation under basic conditions, pH> 12, produces a layered manganese oxide precursor. The precursor is ion exchanged and then calcined at elevated temperatures, generally above 600 ° C., to form the OMS-2 product. Analytical tests showed that the OMS-2 produced by this method is 800
It is thermally stable up to ° C, indicating a lower average oxidation state of manganese ions.

Todorokiite is a naturally occurring manganese oxide having a (3 × 3) tunnel structure formed by the triple chains of MnO ₆ edge-sharing octahedra. Todorokites and related species are described by Turner et al. In “Todorokites: AN
ew Family of Naturally Occurring Manganese Oxide "
Science, Vol. 212, pp. 1024-1026 (1981). The authors found that todorokites are often found in deep-sea manganese nodules containing high concentrations of copper and nickel, so that such metals were found to have Mn ^{+2 in} octahedral frameworks.
I suspect that it may be replaced by.

Todorokites are of particular interest because of their relatively large tunnel size and their cation exchange behavior similar to that of zeolites (Shen et al.,
"Manganese Oxide Octahedral Molecular Sieves: Pre
paration, Characterization, and Applications '' Scie
nce, Vol. 260, pp. 511-515 (1993)). Naturally occurring todorokiite is poor in crystallinity, impure in composition, and coexists with other manganese oxide minerals. High-resolution transmission electron microscopy (HRTEM) results show that todorokites contain random intergrowths of 3x2, 3x3, 3x4 and 3x5 tunnel structures. Todorokites show altered and non-reproducible catalytic activity, a drawback that hampers their commercial use due to their irregular structure.

A method of synthesizing a manganese oxide octahedral molecular sieve having a (3 × 3) tunnel structure as in naturally occurring todorokite is disclosed in US Pat.
40,562. Such a synthetic octahedral molecular sieve having a (3 × 3) tunnel structure is referred to in the art by the name OMS-1. The (3 × 3) tunnel structure of OMS-1 is shown schematically in FIG.

OMS-1 is obtained by reacting a manganese cation and a permanganate oxide anion under strongly basic conditions,
A layered manganese oxide precursor is produced, then the precursor is aged at room temperature for at least 8 hours, the aged precursor is ion-exchanged, and the ion-exchanged precursor is added to 150
It can be prepared by pressurizing at ˜180 ° C. for several days. Analytical tests are based on the O produced by this method.
It shows that MS-1 is thermally stable up to about 500 ° C.

It is important to understand that the manganese oxide structure of the present invention is a special type. Manganese oxides can have a variety of structures. According to the literature (Burns, RG; Burns, VM, Review in Minera
logy, Amer. Mineral Soc., Chap. 2, Vol. I, 1979
), Manganese oxides are usually large in variety, complicated in properties, poor in crystallinity, intergrowth with other phases, irregular, and non-stoichiometric. Although 20 or more manganese oxide phases are known, only a few of them have specific structures confirmed.

[0012]

According to the present invention, a manganese oxide material having an octahedral molecular structure is formed: a) forming a solution containing permanganate oxide anions; b) adding an organic reducing agent to the solution. Formed to form a gel; c) recovering the gel substantially free of unreacted reducing agent; d) produced by a method comprising heating the gel at a temperature effective to produce a manganese oxide material. It

The manganese oxide material produced by the sol-gel method of the present invention is a layered material such as busselite.
erite) or birnessite, which can be used as precursors in the production of OMS-1 and / or OMS-2. Layered materials are crystalline structures in which the atoms are largely grouped together in a set of parallel planes with the region between the planes being relatively empty.

Alternatively, the material can be a three-dimensional structure commonly referred to in the art as an octahedral molecular sieve. It has been found that the manganese oxide material produced by this method has thermal stability up to 800 ° C. Thus, the octahedral molecular sieve produced by the sol-gel method of the present invention was shown to have significantly higher thermal stability than the octahedral molecular sieve produced by the hydrothermal method. Therefore, the manganese oxide material produced by the method of the present invention can be used in catalytic reactions carried out at elevated temperatures, ie above 600 ° C. In addition to significantly expanding the applicability of manganese oxide materials, several other advantages offered by this sol-gel method include controlling the resulting phase, and easy incorporation of dopants and templating agents,
The production of thin films has been carried out, the manganese oxide material has been synthesized on a molecular scale to give a very pure product, the ability it provides to control the particle and pore size of manganese oxide octahedral molecular sieves, and also its There is a relatively inexpensive treatment.

As used herein, "OMS" is understood to refer to substituted and unsubstituted synthetic manganese oxide octahedral molecular sieves.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION To carry out the sol-gel method of the present invention, first, a solution containing a permanganate oxide anion is formed. The solution is preferably formed by dissolving permanganate in an aqueous medium such as distilled deionized water. The permanganate is not particularly limited as long as it is soluble in an aqueous medium. Generally, the permanganate can be an alkali or alkaline earth metal permanganate, such as sodium, potassium, cesium, magnesium, calcium, barium, or a combination thereof. Permanganates of potassium, cesium and barium have been found to be particularly useful. The concentration of permanganate oxide anion in the solution is not limited to a narrow range,
1M or less is generally preferable, and 0.35M or less is particularly preferable.

After the permanganate is dissolved, the organic reducing agent is added to the solution with stirring. The organic reducing agent is also not particularly limited as long as it does not prevent the formation of gel. Suitable organic reducing agents include, for example, maleic acid, fumaric acid, glutaric acid, phthalic acid, glucose, sucrose, alcohols and combinations thereof. Suitable alcohols include, for example, ethylene glycol, glycerin, polyvinyl alcohol and allyl alcohol. The molar ratio of permanganate anion to organic reducing agent is generally 1.5: 1 to 4: 1, preferably 2: 1 to 3: 1.
Range. A sol forms almost immediately upon addition of the organic reducing agent. In a relatively short time, for example, less than 30 minutes, the sol starts to gel and at the same time syneresis occurs. The reaction temperature is generally in the range of 0 to 60 ° C, preferably 5
Is in the range of -30 ° C.

When recovering the gel, it is important to remove the unreacted reducing agent. This causes the final manganese oxide octahedral product to have an oxidation state higher than that of a similar material without the reducing agent removed.

The gel can be recovered from the reaction medium by any suitable technique. Generally, the gel is washed several times with purified water and the wash water is decanted. The gel can then be filtered, for example in a filter funnel, under reduced pressure for a suitable period of time at room temperature. The gel is then dried, preferably in an oven at 100 ° C. for 10 hours.

Next, the recovered gel product is dried in air to 40
Heat at 0-900 ° C. to obtain the desired manganese oxide material. Preferably, temperatures in the range of 450-800 ° C are used. This heating step, or firing step, is typically 0.1
~ 24 hours, preferably 1-6 hours.

Those skilled in the art will appreciate that the doping and templating agents,
For example, transition metal cations, organic amine cations and inorganic cations may be added to the sol to control the pore structure of the resulting manganese oxide material, and its skeleton and / or tunnel structure to be one or more metal cations, such as alkali metals, It will be appreciated that the cations of the alkaline earth and transition metals may be substituted.

[0022]

The octahedral molecular sieve produced by the method of the present invention has acid sites including Lewis acid sites and Bronsted acid sites. Applications include catalytic reactions such as isomerization and polymerization, and adsorption. Specific examples of the use of catalytic reaction and adsorption of OMS include decomposition of alcohol, oxidation of CO, dehydrogenation of hydrocarbons, reduction of NO, hydrogenation of olefins, demetallization of petroleum residual oil, of organic sulfur compounds. Decomposition, decomposition of organic nitrogen compounds, decomposition of asphalt, adsorption of harmful gases and adsorption of heavy metal ions.

[0023]

EXAMPLES The following non-limiting examples illustrate specific embodiments of the present invention.

Example 1: Preparation of potassium barnesite layered manganese oxide material by sol-gel technique. In a 125 ml Erlenmeyer flask, 5.0 g glucose was dissolved in 20 ml distilled deionized water to give 1.4 M glucose. A solution was prepared. In a 150 ml beaker,
A 0.38M solution of KMnO ₄ was prepared by dissolving 3.0 g of KMnO _{4 in} 50 ml of distilled deionized water.
The purple KMnO ₄ solution was added to the colorless glucose solution. As a result, an exothermic reaction occurred and, upon stirring, a uniform red sol was formed. After a few seconds the sol turns brown and 1
Within minutes, it turned into a brown gel. Run this gel at room temperature for 1
After cooling for 5 to 30 minutes, it was dried at 110 ° C. After about 24 hours, a sticky, brown xerogel was obtained. The xerogel was placed in an alumina boat and placed in air for 450
The xerogel was converted to a gray-black ash by firing for 2 hours at 0 ° C., which was immediately ground into a fine black powder. X-ray diffraction analysis of this powder revealed a characteristic peak of the compound having the potassium barnesite structure. The positions of peaks and the approximate relative intensities were as follows. 7.1Å (100);
3.5Å (50); 2.5Å (10); 2.4Å (2
0); 2.2Å (10); 2.1Å (10); 1.8Å
(10)

This procedure was carried out using sucrose instead of glucose, resulting in substantially the same reaction and the same potassium barnesite material. Using other polyalcohols such as ethylene glycol, glycerin, polyvinyl alcohol, allyl alcohol,
A similar reaction was observed.

Example 2: K-OM by sol-gel technique
Preparation of S-2 To a 0.1M solution prepared by dissolving 1.5804 g of KMnO ₄ (manufactured by JD Baker) in 100 ml of distilled deionized water, 0.387 g of maleic acid (manufactured by Pfalts and Bauer) was added. The mixture was stirred for 30 minutes. A dark brown sol formed at room temperature, which began to gel within 5-10 minutes with immediate syneresis. The resulting H ₂ O / gel product was H ₂ O in the upper 50% by volume of the gel. The H ₂ O was decanted. The gel obtained was washed 4 to 5 times with 100 ml of distilled deionized water, and the wash water was decanted. The gel was then transferred to a filter funnel (water aspirator) and filtered under reduced pressure at room temperature for 20 minutes. The gel was placed in an oven and heated in air at 100 ° C. for about 10 hours. Then, the dried gel was heated in air at 450 ° C. for 4 hours. The X-ray powder diffraction data is presented in Table 1 below and in FIG.

[0027]

[Table 1]

The X-ray powder diffraction data shown in Table 1 and FIG. 3 show that naturally occurring cryptomelane, KMn.
_It is in good agreement with the diffraction data of ₈ O ₁₆ .

FIG. 4 represents the thermogravimetric analysis (TGA) of the OMS-2 gel prepared in Example 2. The weight change from room temperature to 200 ° C is due to the loss of H ₂ O,
At 500 ° C it is due to the decomposition of organic acids,
At 500-550 ° C it is due to the formation of OMS-2 and at 800-900 ° C it is due to OMS-2.
Those of the oxidation of Bikusubi to ore (Mn ₂ O ₃ cubes). Using Fourier transform infrared spectroscopy data, H
The loss of ₂ O and maleic acid was confirmed and confirmed. These data demonstrate that the octahedral molecular sieves produced by the method of the present invention are thermally stable up to about 800 ° C.

The temperature programmed desorption data (TPD) for O ₂ generated when the OMS-2 gel is heated from room temperature to 500 ° C. is shown in FIG. In the case of this substance, the integration of the TPD data is as follows:
This shows that only 0.48 oxygen atoms were generated. In contrast, calcined OMS produced by hydrothermal method-
2 resulted in the loss of 9.41 oxygen atoms. The thermal stability of the sol-gel OMS-2 system is clearly superior to that of the material produced by the hydrothermal method.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a tunnel structure of OMS-2.

FIG. 2 is a schematic diagram showing a tunnel structure of OMS-1.

FIG. 3 is a diagram showing an X-ray powder diffraction pattern of OMS-2 produced by the method of the present invention.

FIG. 4 shows the results of thermogravimetric analysis of OMS-2 produced by the method of the present invention.

FIG. 5 is a diagram showing the temperature programmed desorption of O ₂ of OMS-2 produced by the method of the present invention.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Niangero Duane, Connecticut 06268, USA, Storrs, Northwood Apartments 64 (72) Inventor Steven Lawrence Swift, Connecticut 06258, Storrs, Hanks Hill Road 88

Claims (2)

[Claims] 1. A method for producing a manganese oxide material having an octahedral molecular structure, comprising: a) forming a solution containing a permanganate oxide anion; b) adding an organic reducing agent to the solution to form a gel. C) recovering a gel substantially free of unreacted reducing agent; d) heating the gel at a temperature effective to produce a manganese oxide material. 2. The method according to claim 1, wherein the manganese oxide material is a manganese oxide octahedral molecular sieve having a 2 × 2 tunnel structure.